1. Field of the Invention
The present invention relates to a voice synthesizing method, a voice synthesizing apparatus, and a semiconductor device including a voice synthesizing apparatus as well as a computer readable program to be executed for implementing a voice synthesis.
2. Description of the Related Art
In the prior arts, it has been known that the voice synthesizer produces a voice sound and a voice-less sound in different methods respectively, along the voice generation models. For example, a vocoder inputs a pulse in accordance with a pitch frequency for producing the voice sound, while using a white noise for producing the voice-less sound. This generation method may be implemented by using a digital signal processing. In this case, a common output device may be used for producing both the voice sound and the voice-less sound, wherein respective sampling frequencies for producing the voice and voice-less sounds are the same as an output sampling frequency of the common output device.
By observing a waveform of a voice sound spoken by a human, it is confirmed that a power of the voice sound is concentrated in a lower frequency band than that of a power of the voice-less sound. The optimum sampling frequency for producing the voice-less sound is too high to produce the voice sound. This leads to disadvantageous in that a waveform-editing voice synthesizing method needs a larger storing capacity for storing waveform fragments. Storing the voice waveform fragments often needs a larger capacity than storing the voice-less waveform fragments. Increase in the storage capacity is the trade-off for the size down of the voice synthesizer.
The use of the commonly uniform sampling frequency for both the voice sound and the voice-less sound has the above-described disadvantage in the trade-off between the optimization to the sampling frequency for producing the voice-less sound and the reduction to the storage capacity.
Japanese laid-open patent publication No. 60-113299 discloses processes for separately setting respective sampling frequencies of the voice sound and the voice-less sound, wherein a clock frequency to be used for reading out a waveform of a voice-less consonant is made varying in accordance with tone data. This second conventional technique is, however, disadvantageous in that the tone of the voice-less consonant varies depending on the tone data.
Japanese laid-open patent publication No. 58-219599 discloses that the voice fragments are held at the low sampling frequency for data interpolation in the voice synthesizing process in order to make the sampling frequency higher apparently, thereby obtaining a good tone synthesized voice. This third conventional technique is, however, disadvantageous in that holding the voice fragments at the low sampling frequency makes cut the voice component at the high frequency band.
In the above circumstances, the developments of novel method and apparatus for performing voice-synthesis with good tones without increasing the required storage capacity free from the above problems is desirable.